Close-Proximity Applications
Close-proximity communications are used in a variety of applications that promote identification, authentication, payment, tolls, various logistics and the like to establish and manage the “internet-of-things.” RFID (Radio Frequency Identification) close-proximity applications include: low frequency (LF) applications, such as animal identification, that utilize frequencies between 120 and 150 kHz, high frequency (HF) applications, such as smart cards that frequently use frequencies at 13.56 MHz, ultra high frequency (UHF) applications, such as active tags, that use a frequency of 433 MHz, other ultra high frequency (UHF) applications, such as passive toll tags that utilize ISM (Industrial, Scientific and Medical) frequency bands with frequencies from 865 to 928 MHz, microwave frequencies, such as 2.45 to 5.8 GHz, and ultra wideband (UWB) frequencies from 3.1 to 11 GHz. Other close-proximity standards include the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the Bluetooth® band at 2.4 GHz. Emerging standards such as NFC (near-field communication) have also become popular for transferring data from NFC-enabled devices to close-proximity readers using 13.56 MHz as a carrier frequency.
Miniature Tunable Antennas
Consumer demand for smaller wireless devices is pushing for smaller compact antennas. As the antenna size is reduced, the bandwidth and number of frequency bands a compact antenna can support becomes more challenging. A number of approaches have been attempted to make antennas tiny and tunable over multiple frequencies. Since mobile devices are typically small in size, keeping antennas sensitive at small apertures is a challenge. Typical miniature antennas include loop and dipole spiral antennas and variations thereof.
U.S. Pat. No. 7,714,794 describes a folded dipole spiral antenna with a loop section for RFID applications.
Approaches to make antennas tunable over multiple frequencies include published US patent application 2012/0231750, which describes a loop antenna formed from portions of a conductive bezel and a ground plane. Prior art references such as these attempt to make the antenna structure tunable using variable capacitors and inductive elements across the antenna feed terminals or across antenna structural components.
Other representative sample prior art references include U.S. published patent application 2010/0283688 that discloses a multiband folded dipole transmission line antenna including a plurality of concentric-like loops, wherein each loop comprises at least one transmission line element, and other antenna elements.
US published application 2010/0231461 discloses a modified monopole antenna electrically connected to multiple discrete antenna loading elements that are variably selectable through a switch to tune the antenna between operative frequency bands.
U.S. Pat. No. 7,576,696 discloses the use of multiple assemblies consisting of arrays of discrete antenna elements to form an antenna system that selectively filters electromagnetic bands.
US published patent application 2009/0278758 discloses a multiband folded dipole structure containing two electrically interconnected radiating elements wherein one of the radiating elements has capacitor pads that couple with currents from the other radiating element to produce the “slow-wave effect”.
US published patent application 2008/0007461 discloses a U-shaped multiband antenna that has internal reactance consisting of a ceramic or multilayer ceramic substrate.
US published patent application number 2007/0188399 discloses a selective frequency dipole antenna consisting of a radiator comprising conductor regions that have alternating shapes (zig-zag or square meander lines) with an interleaving straight line conductor section, as well as a multiband antenna dipole antenna consisting of a plurality of radiators so constructed, which may be deployed with and without coupling to capacitive or inductive loads.
U.S. Pat. No. 7,394,437 discloses the use of multiple microstrip dipole antennas that resonate at multiple frequencies due to “a microstrip island” inserted within the antenna array.
U.S. Pat. No. 7,432,873 discloses the use of a plurality of printed dipole antenna elements to selectively filter multiple frequency bands.
U.S. Pat. No. 7,173,577 discloses dynamically changing the composition of a fluidic dielectric contained within a substrate cavity to change the permittivity and/or permeability of the fluidic dielectric to selectively alter the frequency response of a phased array antenna on the substrate surface.
U.S. Pat. No. 7,053,844 discloses a multiband dipole antenna element that contains radiator branches.
US published patent application 2005/0179614 discloses the use of a microprocessor controlled adaptable frequency-selective surface that is responsive to operating characteristics of at least one antenna element, including a dipole antenna element.
U.S. Pat. No. 6,943,730 discloses the use of one or more capacitively loaded antenna elements wherein capacitive coupling between two parallel plates and the parallel plates and a ground plane and inductive coupling generated by loop currents circulating between the parallel plates and the ground plane is adjusted to cause the capacitively loaded antenna element to be resonant at a particular frequency band and multiple capacitively loaded antenna elements are added to make the antenna system receptive to multiple frequency bands.
U.S. Pat. No. 6,717,551 discloses the use of one or more U-shaped antenna elements wherein capacitive coupling within a U-shaped antenna element and inductive coupling between the U-shaped antenna element and a ground plane is adjusted to cause said U-shaped antenna element to be resonant at a particular frequency band and multiple U-shaped elements are added to make the antenna system receptive to multiple frequency bands.
US published patent application 2004/0222936 discloses a multi-band dipole antenna element that consists of metallic plate or metal film formed on an insulating substrate that comprises slots in the metal with an “L-shaped” conductor material located within the slot that causes the dipole to be resonant at certain select frequency bands.
U.S. Pat. No. 6,545,645 discloses the use of optical interference between reflective antenna surfaces to select specific frequencies within a range of electromagnetic frequencies.
U.S. Pat. No. 6,147,572 discloses the use of a micro-strip antenna element co-located within a cavity to form a device that selective filters frequencies from a range of electromagnetic frequencies.
U.S. Pat. No. 5,917,458 discloses a frequency selective dipole antenna that has frequency selectivity by virtue of being integrated upon the substrate that is designed to operate as a frequency selective substrate.
U.S. Pat. No. 5,608,413 discloses an antenna formed using co-located slot and patch radiators to select frequencies and alter the polarization of radiation emissions.
U.S. Pat. No. 4,513,293 discloses an antenna comprising a plurality of parabolic sections in the form of concentric rings or segments that allow the antenna to use mechanical means to select specific frequencies within a range of electromagnetic frequencies.
Other approaches such as U.S. Pat. No. 5,220,339 involve using materials such as amorphous metal as a core with an electric conductive material wound around the length of the antenna element in order to receive VHF and UHF frequencies.
Close-Proximity Devices with a Magnetic Stripe
Similar to RF based close-proximity communications, magnetic stripe technology is a popular method to embed information onto a device and transfer data to another device via a close-proximity magnetic card reader or magnetic stripe reader, collectively called “magnetic card reader” hereafter. Governed by ISO/IEC (International Organization for Standardization and the International Electrotechnical Commission) standards such as 7810, 7811, and 7813, various types of information can be such as bank information, identity information, or other account information can be programmed or written onto a magnetic stripe by alternating the orientation of magnetic particles on a magnetic stripe. As the card is swiped, one or more heads on a magnetic card reader receives the alternating polarity of the magnetic field from the programmed magnetic stripe on the card. Magnetic stripe technology has been widely accepted in a broad number of markets including payment, identity, authentication, loyalty/reward, hotel/motel, and other industries due in part to its reliability, ease-of-use, its relative low expense to manufacture to size of a thin card.
Dynamic Magnetic Stripe Emulation
Several approaches have attempted to replicate information stored on common magnetic stripe and transmit this data to a magnetic card reader which then receives the data just as it would from a traditional magnetic stripe card. These methods are often referred to as dynamic magnetic stripe, or magnetic stripe emulation. Most of these approaches involve coils that send information collected from a magnetic stripe card in a manner that duplicates the alternating polarity of the magnetic field that magnetic card readers receive from a typical magnetic stripe card moving through the reader.
One of the earliest prior art that investigated methods to emulate information stored on a common magnetic stripe readable by existing card readers is described in U.S. Pat. No. 4,701,601 (1987). This patent describes a transaction card having a magnetic stripe emulator where the emulator may be a transducer defined by one electromagnetic coil.
Another example of early prior art is U.S. Pat. No. 4,791,283 (1988), which describes a card using magnetic material to couple the magnetic field from a coil where a diamagnetic gap in the magnetic material causes the magnetic field lines across the gap to extend the field from the card, further improving the transmission of the magnetic field.
U.S. Pat. No. 8,690,059 describes yet another coil based magnetic stripe emulation device consisting of a rectangular wound coil acting as an open air core inductor along with a driver that receives signals from an external source, conditions and amplifies the power of the electrical information so that it can be transmitted magnetically from a cell phone.
Other prior art includes “payment cards” that comprise a common coil. U.S. Pat. No. 8,608,083 (2013) is an example of several patents that describe payment cards that use various coils to emulate the magnetic stripe, as do patent applications WO 2007/028634 A1, and WO 2002/047019 A1.
U.S. Pat. No. 8,302,871 (2012) describes yet another payment card that uses coils of ferromagnetic core to emulate two tracks of a magnetic stripe.
Patent application WO 1996/026500 A1 describes a magnetic stripe card simulation means with at least one electrical coil, but where that coil is wound around a u-shaped core.
Wake-Up Methods
Many RFID applications such as tolls and NFC utilize antennas matched to a specific resonant frequency to detect a close-proximity reader and activate a circuit in response. These circuits are considered to be passive, or semi-passive if a battery then takes over powering the circuit after initial wake-up. An issue with these approaches is that any signal received at a resonant frequency of the antenna will activate the circuit. For other close-proximity applications such as magnetic stripe, the reader can be detected and the speed of swiping a card a magnetic stripe can be determined using methods involving phase and/or capacitive sensing as described in U.S. Pat. No. 8,317,103.
Battery Charging
Other prior art references describe methods to perform inductive charging of batteries, although these methods are typically employ dedicated apparatuses defined inductive power standards such as Qi.